What about Flash?

Macromedia is pushing CFMX and Flash MX as a Rich User Interface.

Flash MX does have some accessibility built in.

Flash Player 6 now uses the Microsoft Active Accessibility (MSAA) API to exchange information with a web browser that supports MSAA, which channels information to and from assistive technologies that support MSAA.

Today, the only screen reader that allows users to interact with Flash content is Windows-Eyes from GW Micro.